Abstract
Isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether), C3H2ClF5O, is a commonly used inhalation anaesthetic. Using a proton transfer reaction mass spectrometer (PTR-MS) we have detected isoflurane in the breath of patients several weeks following major surgery. That isoflurane is detected in the breath of patients so long after being anaesthetised raises questions about when cognitive function has fully returned to a patient. Temporal profiles of isoflurane concentrations in breath are presented for five patients (F/M 3/2, mean age 50 years, min–max 36–58 years) who had undergone liver transplant surgery. In addition, results from a headspace analysis of isoflurane are presented so that the product ions resulting from the reactions of H3O+ with isoflurane in PTR-MS could be easily identified in the absence of the complex chemical environment of breath. Six product ions were identified. In order of increasing m/z (using the 35Cl isotope where appropriate) these are (m/z 51), CHFCl+ (m/z 67), CF3CHCl+ (m/z 117), C3F4OCl+ (m/z 163), C3H2F4OCl+ (m/z 165), and C3F4OCl+ H2O (m/z 183). No protonated parent was detected. For the headspace study both clean air and CO2 enriched clean air (4% CO2) were used as buffer gases in the drift tube of the PTR-MS. The CO2 enriched air was used to determine if exhaled breath would affect the product ion branching ratios. Importantly no significant differences were observed, and therefore for isoflurane the product ion distributions determined in a normal air mixture can be used for breath analysis. Given that PTR-MS can be operated under different reduced electric fields (E/N), the dependence of the product ion branching percentages for isoflurane on E/N (96–138 Td) are reported.
Highlights
In a recent paper we reported a study of the volatile biomarkers in breath associated with liver disease using proton transfer reaction mass spectrometry (PTR-MS) [1]
The risk of false discovery was minimised by using a two stage process to reduce the variable set so that we did not have to rely on unsupervised multivariate analysis. For this present work 12 of the 31 patients investigated in the first stage, which involved comparing breath samples of patients suffering with chronic liver disease with 30 healthy controls, had their breath analysed post liver transplant
Prior to being able to analyse the mass spectra of the post-transplant breath samples, it was necessary to establish which product ions result from the reaction of H3O+ with isoflurane in the drift tube environment of a PTR-MS, divorced from the complex chemical environ ment of breath
Summary
R Fernández del Río1, M E O’Hara1, P Pemberton2, T Whitehouse2 and C A Mayhew1,3 Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Keywords: proton transfer reaction mass spectrometry, isoflurane anaesthesia, alveolar breath analysis, cognitive function, volatile organic compounds Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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